Rotors of turbomachines, for example compressors, gas turbines or steam turbines, carry blading consisting of a multiplicity of rotor blades which are inserted into circumferentially extending grooves and retained there. Particularly gas turbine rotors, which are reconditioned for extending the service life, must be frequently hollowed out in the grooves in order to remove worn material (e.g. rust, products of corrosion).
It is the aim in this case that the material becomes “clean” again (and therefore capable of supporting the blading) and that the rotor can go into operation again with new blades and can be operated in an operationally reliable manner until the next inspection.
As a result of the hollowing out of the worn grooves, which become larger, deeper and wider; the grooves obtain a large diameter. This can be compensated by means of specially manufactured rotor spacers. (Rotor spacers are “relatively” inexpensive in comparison to the blades).
The blades themselves are also to be adapted in this respect, but would be time-consuming, costly and lead to further blade variants with subsequent costs for storing, logistics, management, replacement part supply, etc. The production of blade variants for reconditioned rotors should therefore be avoided as far as possible.
For this reason, attempts are frequently made to limit the hollowing out of grooves to a minimum since otherwise the rotor blades acquire an excessively large radial and axial clearance in the grooves.
Consequently, the effectiveness of the hollowing out and of the repair of the rotors is limited, however.
Severely damaged rotors can no longer be hollowed out in this way. A repaired rotor with an excessively large blade clearance can no longer be operated in an operationally reliable manner.